1. Field of the Invention
The present invention relates to a shoe, in particular a sports shoe with a cushioning system.
2. Background Art
Shoe soles are subjected to substantial compressive loads. Particularly in sports shoes, there are ground reaction forces resulting when the shoe contacts the ground with the heel and during push-off at the end of the step cycle exceed the body weight. Accordingly, a sole construction must on the one hand provide a sufficient cushioning comfort to avoid premature fatigue or even injuries of the muscles or the bones. On the other hand, it must be capable to withstand these forces over an acceptable lifetime.
In sports shoes, for example running shoes, cushioning elements made out of foamed materials such as ethylene-vinyl-acetate (EVA) are typically arranged in the sole. Although this material provides good cushioning properties, it has a limited lifetime. For example runners with a high monthly mileage must replace their running shoes after only a few months. Further disadvantages are the temperature dependency of the cushioning properties of EVA and the comparatively high weight.
Therefore, applicant developed shoe soles in the past, for example those disclosed in DE 102 34 913 A1 and DE 10 2005 006 267 B3, wherein the conventional foamed cushioning elements are at least partly replaced by structural deformation elements without EVA. The disclosures of DE 102 34 913 A1 and DE 10 2005 006 267 B3 are incorporated in their entirety herein by reference thereto. However, the structural deformation elements tend to be slightly stiff and in a similar manner to foamed EVA cushioning elements only provide a limited cushioning movement. From a theoretical point of view, the complete height at which the foot is positioned above the ground surface is available for a cushioning movement, for example, during ground contact with the heel. Practically, however, only a fraction of the distance to the ground can actually be used for the cushioning movement, since the compressed cushioning material takes up a significant residual volume below the sole of the foot. As a result, there might be a so called “bottoming out”, in case of peak loads, if the cushioning material is fully compressed which excludes any further cushioning movement. If the initial volume is increased, the shoe becomes unstable and a spraining to the side may cause severe injuries. Furthermore, the increased amount of cushioning material leads to a greater weight of the shoe, which is undesirable for most sports shoes.
U.S. Pat. No. 4,894,934 to Illustrato discloses an arrangement for the heel part of a shoe wherein two leaf spring-like surfaces are pivotably attached to each other. The centers of the two surfaces are interconnected by a rubber element which is elongated under a compression of the heel part and thereby provides a restoring force. This design is very complex and leads to a substantial residual volume which restricts the available cushioning movement.
U.S. Pat. No. 6,553,692 to Chung discloses a complex arrangement for the heel part of a shoe which transforms a compression movement in the sole into a compression or elongation of a horizontally arranged coil spring. Also here there is a significant residual volume of the cushioning system so that the explained difficulties are not avoided. Furthermore, the design is so complex that it is inconceivable to economically manufacture the corresponding shoe.
U.S. Published Application No. 2006/0065499 to Smaldone et al. discloses an arrangement having several toggle levers transforming a compression in the heel of a shoe into a linear movement so that a star-like elastic element is radially elongated. The design of the toggle levers is complex and requires the assembly of a plurality of straight rods having lugs at their ends for receiving a plurality of axles. Furthermore, the star-like elastic element is arranged exactly in the center of the construction between the outer surfaces of the cushioning element. In this position it can easily be damaged and causes an accumulation of dirt which impairs the cushioning movement.
Embodiments of the present invention are therefore based on the problem to provide a shoe with a cushioning system, which can be cost-efficiently manufactured and which overcomes the above mentioned disadvantages of the prior art by using a greater part of the given thickness of a sole for a cushioning movement.